Sedimentary facies and lithologic oil pools of the Upper Cretaceous Qingshankou Formation in Daqingzijing area,Changling Sag,southern Songliao Basin

Daqingzijing area is a synclinal structure in the central part of Changling Sag.With the Qing-1 member of Qingshankou Formation as the main target zone,Daqingzijing oilfield is discovered with reserves of 100m tons.The reservoirs are mainly derived from Tongyu to Baokang deltaic depositional system,and the sedimentary environment from Qing-1 to Qing-3 members transforms from deep-lake type to shallow-lake type.The sedimentary environments of Qing-1 and Qing-2 members are similar,and with the deep-lake type delta front subfacies developed.The facies belts are fluvial-dominated sandbars and underwater distributaries channel micro-facies with their distributions being multiple and independent in plane as well as narrow-banded in source direction,which is favorable for forming large-scale lithologic deposits.Comprehensive analysis indicates that Qing-2 member has a potential of 50m tons reserves,and is the main target for exploration of the next step.